I thought it was an interesting premise, where Ten is going back to clean up a problem he, The Doctor, created only to have the situation complicated a bit by having survivors involved. It was an interesting story and the antagonists were creepy for sure.
I usually prefer books where the Doctor has a companion, but this was really good. As @DontBlink wrote, it explores Ten’s character in a really interesting way. The weapon was an interesting thought experiment, and it managed to use it in a great way. The audiobook was also really good, narrated by Russell Tovey.
This. Book. Oh my god this book. It’s one of my favorite NSAs and one of my favorite Doctor Who books. I read it all in one day. I’m pretty sure I have a review on the guide, but I’m also going to add a very spoiler heavy live reaction I posted on Tumblr a few years ago because I still think about it.
Spoilers!
So Gallifrey built that weapon in The Eyeless like 100%. There’s tons of evidence (mostly the way the doctor acts in this) but the moment that stood out to me the most was when Asla talked about the four races involved in everything going on, and ten corrects her and says three. And Asla says something along the lines of “No, there’s four. The eyeless, us, whoever made the weapon, and whoever you are.” And ten says, “Ah. If you’re counting that way then that’s right.” I’d even go a step further and say the doctor was involved pretty directly in some way with whatever thing happened originally based on the interactions between them and some of the ghosts. I’m pointing out some pretty obvious things but I’m so obsessed with the concept that I need to talk about it. Especially the way it’s never explicitly confirmed. I think I like that even more than if they’d gone into it.
Somebody also pointed out to me that the fourth group could have been Faction Paradox, which I know very little about. Or it could be a fourth completely unrelated group. Honestly the speculation is the fun part.